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    SubjectRe: [RFC][PATCH 2/6] memcg: add pc_set_mem_cgroup_and_flags()
    From
    On Wed, Apr 18, 2012 at 12:23 AM, KAMEZAWA Hiroyuki
    <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    > (2012/04/18 6:17), Ying Han wrote:
    >
    >> On Wed, Mar 28, 2012 at 3:51 AM, KAMEZAWA Hiroyuki
    >> <kamezawa.hiroyu@jp.fujitsu.com> wrote:
    >>> Consolidate a code for setting pc->mem_cgroup and USED bit which requires smp_wmb().
    >>> And remove a macro PCGF_NOCOPY_AT_SPLIT which isn't helpful to read code, now.
    >>>
    >>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    >>> ---
    >>>  include/linux/page_cgroup.h |   18 ++++++++++++++++++
    >>>  mm/memcontrol.c             |   18 ++++--------------
    >>>  2 files changed, 22 insertions(+), 14 deletions(-)
    >>>
    >>> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
    >>> index 92768cb..2707809 100644
    >>> --- a/include/linux/page_cgroup.h
    >>> +++ b/include/linux/page_cgroup.h
    >>> @@ -1,6 +1,8 @@
    >>>  #ifndef __LINUX_PAGE_CGROUP_H
    >>>  #define __LINUX_PAGE_CGROUP_H
    >>>
    >>> +#include <linux/smp.h>
    >>> +
    >>>  enum {
    >>>        /* flags for mem_cgroup */
    >>>        PCG_LOCK,  /* Lock for pc->mem_cgroup and following bits. */
    >>> @@ -94,6 +96,22 @@ pc_set_mem_cgroup(struct page_cgroup *pc, struct mem_cgroup *memcg)
    >>>        pc->mem_cgroup = memcg;
    >>>  }
    >>>
    >>> +static inline void
    >>> +pc_set_mem_cgroup_and_flags(struct page_cgroup *pc, struct mem_cgroup *memcg,
    >>> +                       unsigned long flags)
    >>> +{
    >>> +       pc->mem_cgroup = memcg;
    >>> +       /*
    >>> +        * We access a page_cgroup asynchronously without lock_page_cgroup().
    >>> +        * Especially when a page_cgroup is taken from a page, pc's mem_cgroup
    >>> +        * is accessed after testing USED bit. To make pc's mem_cgroup visible
    >>> +        * before USED bit, we need memory barrier here.
    >>> +        * See mem_cgroup_add_lru_list(), etc.
    >>> +        */
    >>> +       smp_wmb();
    >>> +       pc->flags = flags;
    >>> +}
    >>> +
    >>>  #else /* CONFIG_CGROUP_MEM_RES_CTLR */
    >>>  struct page_cgroup;
    >>>
    >>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    >>> index 8077460..d366b60 100644
    >>> --- a/mm/memcontrol.c
    >>> +++ b/mm/memcontrol.c
    >>> @@ -2511,16 +2511,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *memcg,
    >>>                }
    >>>        }
    >>>
    >>> -       pc_set_mem_cgroup(pc, memcg);
    >>> -       /*
    >>> -        * We access a page_cgroup asynchronously without lock_page_cgroup().
    >>> -        * Especially when a page_cgroup is taken from a page, pc's mem_cgroup
    >>> -        * is accessed after testing USED bit. To make pc's mem_cgroup visible
    >>> -        * before USED bit, we need memory barrier here.
    >>> -        * See mem_cgroup_add_lru_list(), etc.
    >>> -        */
    >>> -       smp_wmb();
    >>> -       SetPageCgroupUsed(pc);
    >>
    >> I might be confused. We removed this SetPageCgroupUsed() but not
    >> adding it back elsewhere ?
    >>
    >> --Ying
    >>
    >>> +       pc_set_mem_cgroup_and_flags(pc, memcg, BIT(PCG_USED) | BIT(PCG_LOCK));
    >
    >
    > Added here. This sets
    >
    >  | memcg pointer | Used | Locked |

    Ah. I missed that part.

    Thanks

    --Ying

    >
    >
    > Thanks,
    > -Kame
    >
    >
    >
    >
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